Steel alloy



Patented May 31, 1927. r

UNITED STATES PATENT OFFICE.

sTAHLwnRKE AKTIENGESELLSCHAFT nasrnn, GERMANY.

VORM RICH LINDENBERG, 0F REMSCHEID- s'rnnr. ALLOY.

No Drawing. Application filed July 31, 1924, Serial No. 729,370, and in GermanyJanuary 9, 1922.

Among steel alloys which are particularly resistant to disintegration by the atmos phere and by acids, alloys have been proposed, which besides iron contain chromium as an effective component in quantities exceeding 8% and also carbon up to 1%. In general a chromium content of 12 to 20% and a carbon content up to 0.5% is used.

Such alloys are generally termed stainless steel.

It is known that this resistance to the action of acids and the atmosphere (referred to below as rust-proof quality) diminishes eatly when. the carbon content exceeds 0.5%. This disadvantage has been 'over come by the addition of quantities of r .ckel, for instance of 3 to. 10%. One disadvantage of these alloys is that the presence of large percentages of nickel entails the necessity of complicated methods of heat treatment for converting the steel, which shows of itself great hardness connected with considerable toughness, into a state,- inwhich it can be machined. The high nickel content also makes the steel less suitable for certain purposes, more particularly ,for tools with sharp cutting edges.

Neither the chromium steels nor the chromium-nickel steels hitherto known are capable of withstanding the action of nitric acid'with an addition of several per cent of alkali salt (e. g.. chloride). They are 7 also relatively easily attacked by hydrochloric acid and aqua regia. It is known that chromium-iron alloys containing molybdenum are resistant to these agents, these cannot however be regarded as steel alloys but as iron alloys, as these contain carbon only as an impurity (say 0.05%). Such alloys are sufficiently resistant to acids and acid mixtures with a content of alkali, more particularly alkaline chloride, of more than 5%. On the other hand as iron alloys they have the disadvantage that they ,cannot be hardened.

Experiments have shown that it is possible to make a steel alloy which is capable of being readily hardened,'is proof against rust, has great strength, can be readily worked and is far more capable of resisting the action of acids and acid mixtures than. the alloys hitherto known, if to a known from 0.2 to 6%.

steel alloy with 8 to 25% Cr and 0.1 to 1.2% C is added molybdenum in quantities of Manganese and silicon may be present in the usual small quantities. This steel is even capable of resisting the action of boiling aqua regia for a considerable time.

The alloy according 'to the present invention with a content of chromium exceeding 15%, a carbon content up to 0.5% and a content of molybdenum up to 3% may be easily forged. When the content of carbon and molybdenum is greater, the forgeability of the alloy decreases considerably. This disadvantage may be overcome by an addition of 0.5 to 2% Ni or 0.5 to 2% Co or by an addition of both elements up to 3% together. Nickel and cobalt are thus seen to he (as is commoniin the art of alloys) largely. equivalents for each other. The expression nickel-cobalt is intended to cover these two metals. By this addition the rustprooi'ness' is not adversely affected, on the other hand the structure is rendered finer and the strength, more particularly the toughness, is greatly increased. The alloys containing above 0.2%'C are capable of being hardened and with about 0.5% C are specially suitable for cutting tools. When annealed'the alloy may be readily worked or stamped and may be rolled into thin plates or cold-drawn into wire. The annealing of the alloy presents no difiiculties.

The recognition of the fact that the rustproof quality of the alloy depends on the steel being very pure makes a thorough deoxidation necessary. Ithas been found to be preferable to add vanadium or titanium up to 1% to the steel bath for obtaining thorough deoxidation. The two metals, being thus equivalents, tosome extent, can be embraced within the expression vanadiumtitanium group. v

Experiments have shown, that the alloy is also particularly suitable for making cast articles of all kinds, for instance vessels. In order still further to increase the fireresistance of such articles, the content of molybdenum may. be increased up to 10% and the content of nickel or cobalt or. the content of both these elements together up to 15%. of

In this case as well the addition vanadium or titanium to the steel'bath in quantities up to 1% improves the purity "of the steel and increases its resistance to' the action of acids.

What I claim isi .1. A steel alloy, which is highly resistant to chemicalaction and is of great strength,

consisting of iron, 8 to 25% Cr, 0,1 to 1,2%

consisting of iron, 8 to 25% Cr, 0,1 to 1,2% 15 C, 0,2 to 6% Mo, and 0,5 to 3% of nickel and cobalt for increasing the ductility of the alloy when hot.

3. A steel alloy, which is highly resistant,

to chemical-action and is of reat strength, 20

consisting of iron, 8 to 25% 61', 0,1 to 1,2% 0, 0,2 to 6% M0, and 0,5 to 2% of Ni for increasing the ductility of the alloy when hot. v

In testimony whereof I have signed my 25 name to this specification.

DR. ING. WILHELM OERTEL. 

